I find zsh's result lists for Tab completion quite useful, however I'd like to tweak their behaviour a bit:

They should appear when I Tab for the first time and afterwards dynamically update with every new letter added. The default behaviour is that the suggestions are only re-evaluated when you Tab again, I want to save this repeated keypress. (Update: But only list the possible completions, it shouldn't automatically modify my actual prompt line even if there is only one option left.)

You can get quite deep into customizing zsh's behavior. What should happen exactly? At the moment this question reads like you want the choices to be listed for every key press after the initial TAB, but that won't actually complete anything. Should every key press behave as if it was followed by a TAB? Bear in mind that this would mean quite a bit of backspacing for unintended completions.
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user112553Mar 5 '12 at 9:34

@user112553 The first option: In that sense, it shouldn't actually behave like a repeated TAB. I just want the suggestion list to dynamically adjust.
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F30Mar 5 '12 at 14:13

incremental-complete-word
This allows incremental completion of a word. After starting this command, a list of completion choices can be shown after every character you type, which you can delete with ^H or DEL. Pressing return accepts the completion so far and returns you to normal editing (that is, the command line is not immediately executed). You can hit TAB to do normal completion, ^G to abort back to the state when you started, and ^D to list the matches.